1. Field of the Invention
This invention relates to a method and a printer for printing heat sealing labels, more particularly, to a method and a printer optimized for printing product names, dates, bar codes and the like on heat sealing labels.
2. Description of the Prior Art
Adhesive coated labels come in two general types. In one type, a large number of labels are provisionally attached to a backing strip whose surface has been treated with silicone and the labels are individually peeled off the backing strip and attached to the objects to be labeled. In the other type, known as the heat sealing label, the back surfaces of the labels are coated with an adhesive and the labels are attached to the objects to be labeled after the adhesive has been heated and fused into an adhesive state by a heater.
Since the first-mentioned type uses a backing strip which has to be disposed of after the labels have been peeled off, it is both expensive and wasteful of natural resources. In contrast, the heat sealing label has the major advantages of being low in cost and environmentally friendly.
Up to now, however, heat sealing labels have been used only by the method of printing them with a printer beforehand and then, at the time of use, fusing their adhesive to an adhesive state with heat before applying them to the objects to be labeled. Specifically, it has not been possible to print heat sealing labels using a label printer of the thermal or thermal transfer type. This is because the 60.degree.-80.degree. C. melting point of the carbon ink used as printing ink in thermal and thermal transfer printers is lower than the 80.degree.-100.degree. C. melting point of the adhesive of a heat sealing label. The carbon ink printing on a label printed with a thermal or thermal transfer printer would therefore melt and be degraded if heated to the temperature required to fuse the adhesive of a heat sealing label.
In addition, the melting of the adhesive of cut heat sealing labels takes time because it has to be conducted by surface heating with the label held stationary.
In view of the considerable merits of the heat sealing label in terms of cost and resource saving potential, however, a need exists for the development of a label printer able to print heat sealing labels.
Many recent word processors, computer printers and the like adopt ink jet printers that use nozzles for jetting ink onto the printing surface. The ink used in ink jet printers is made easier to jet from fine nozzles by adding to it a wetting agent that lowers its viscosity. Since the added wetting agent prolongs the time required for the printed ink to dry, however, the ink tends to blot, degrading the quality of the printing.
Because of this, adoption of the ink jet method for the printing of product names, dates, bar codes and the like on labels would lead to various problems. In the absence of some effective countermeasure, the long time required for the ink to dry would be a particular problem in the case of printing bar codes, which cover a large area and need several times longer than ordinary characters to dry. As a result, the label processing speed would be lowered. In addition, there would still be the problem of printing degradation by ink blotting.
Based on a careful study of the heat sealing label technology and the ink jet printing method technology, the inventor discovered that the two technologies can be combined to eliminate each other's drawbacks. This invention was accomplished on the basis of this discovery.
Moreover, since the invention adopts the method of heating cut labels by moving them in contact with a linear heat source, the time required for fusing the adhesive is greatly reduced, whereby the time required for producing labels is shortened.